The present invention relates to granules of inorganic pigments, a process for their production using several auxiliary substances by compacting and their use in many technical fields.
Even in the case of mass products such as inorganic pigments, the use of pigment granules has greatly increased in the last few years for reasons of industrial hygiene, such as dustlessness and toxicity, and improved handling (flow and metering behavior). Spray and accretion granules are known. In spray granulation, spraying from aqueous suspension takes place, and in accretion granulation, accretion in mixers or on rotary tables, for example, with subsequent drying step. These procedures require a great deal of energy. Compacting processes as inexpensive ways of producing granules for mass products again require either high pressures or the use of binders, so that the granules obtained thereby are generally only suitable for specific fields of application such as in building materials or plastics or in emulsion paints.
Spray drying processes for producing granules to color concrete are based on pigment suspensions and use binders. Corresponding processes are described in various industrial rights. Water-soluble binders are used. Organic substances such as lignin sulphonates, formaldehyde condensates, gluconic acids and sulphated polyglycol ethers are used in DE-A-36 19 363, EP-A-0 268 645, U.S. Pat. No. 4,946,505 and EP-A-0 365 046, whereas inorganic salts such as silicate and phosphate are used according to DE-A-39 18 694 and U.S. Pat. No. 5,215,583. A combination of spray and accretion granulation is described in EP-A-0 507 046 (U.S. Pat. No. 5,199,986). DE-A-36 19 363 and EP-A-0 268 645 even expressly exclude compacting processes because too much coherence of the particles is achieved by the use of pressure so that although good transport stability of the granules is achieved, so also are reduced dispersing properties.
EP-A-0 257 423 and DE-A-38 41 848 describe spray granulation with the addition of polyorganosiloxanes as hydrophobic lipophilic additives. The spray dryer mentioned generally leads to small particle sizes, i.e. high fines. A substantial proportion of the material from the dryer cannot therefore be used directly as granules but must be retained as fines in a filter and returned to the process. In the case of spray-granulated products the hydrophobizing post-treatment leads to granules which flow very well but create an extraordinarily large amount of dust.
At high compressive forces, compacting or compression processes lead to granules which are stable but difficult to disperse, and at low compressive forces too much dust is created so that the yield is poor. This is countered by binders or dispersants which bring about both an improved adhesion of the pigment particles to each other and a repellent, stabilizing effect on incorporation into a particular medium such as concrete, asphalt, plastic or emulsion paints.
A process for coloring asphalt with inorganic pigment granules is known from DE-A-42 14 195 and U.S. Pat. No. 5,389,137 in which oils are used as binders. The granules are produced by means of a simple granulation process.
In DE-A-43 36 613 U.S. Pat. No. 5,634,970, U.S. Pat. No. 5,484,481 and DE-A-43 36 612, inorganic pigment granules are produced from pigments by mixing with binders, compacting, crushing and finally forming into granules. These granules have been optimized for use in plastics by means of hydrophobic binders and/or improved by addition of dispersants as far as aqueous systems are concerned.
Granules which were optimized for the individual field of use in question were produced by special production processes and with binders with specific properties.